1. Field of the Invention
The present invention relates to the composition of a machine body of an industrial robot, and more particularly, to the composition of a movable machine body of a high-density installation type robot by which a plurality of robots are able to simultaneously work on an object without interfering with each other, to thereby achieve a desired robot operation with a high efficiency.
2. Description of the Related Art
In recent years, industrial robots have become increasingly used to promote the automation of operations in applications such as an automobile assembly line. In such an automated operation line or the like, a high-density installation method may be used whereby a plurality of industrial robots are installed side by side for working on an object, for example, an automobile, and a desired working area is allotted to each robot to thus ensure an efficient progress of the operation. More specifically, when spot-welding many points on an automotive body, the welding points are divided into a plurality of areas, and each of the robots is assigned one of those areas for spot-welding, to be able to thus spot-weld as many points as possible within a unit of time. The following describes a working area of the high-density installation type robot conventionally used for such a high-density installation type robot operation.
FIGS. 5A and 5B are schematic mechanism diagrams illustrating a mechanism and working area of the conventional high-density installation type robot, wherein FIG. 5A is a side view and FIG. 5B is a top plan view. As shown in FIG. 5A, the first robot arm 1 is provided so that it can turn around the axial center of a joint 2, the second robot arm 4 is provided to allow the second joint 2 of the first robot arm 1 to turn around the horizontal axial center of another joint 3, and a robot trunk 6 is provided which allows the second robot arm 4 to turn around the horizontal axial center at a joint 5. The bottom end of the robot trunk 6 is fixed to an installing surface, and a working end effector 7 attached to the end of the first robot arm 1 is positioned at a desired point in a three-dimensional space by the rotation of the two joints 3 and 5 around the horizontal axial center.
In the conventional high-density installation type robot, however, the end effector installed at the end thereof is moved from one point to another by the rotation of the joints 3 and 5 around the horizontal axial center, and therefore, the moving area in the space becomes a spherical area enclosed with a spherical enveloping surface. More specifically, the moving area of the end effector 7 is inside a three-dimensional space area which extends beyond the robot arms, as enclosed with circular arc solid lines A and B in the side view of FIG. 5A and the top plan view of FIG. 5B. Generally, however, many workpieces, e.g., automobile bodies, on which a high-density installation type robot works have a convex shape midway between a rectangular parallelepiped and a spherical contour, and there are a small number of workpieces having concave contours when observed from the outside space side. Therefore, the convex spherical operating area of the end effector of the robot mentioned above leads to a waste of the area in the robot's end effector operating area when working on such workpieces which have such a contour because there is no correspondence therebetween. More specifically, in the robot movable machine body design, the space extending beyond the robot's arms is also included in the operating area as described above, although only the hatched spaces shown in FIG. 5A and FIG. 5B provide the scope within which the robot can work on objects which are mostly concave. This poses a problem of a large waste of the area, and of a relatively limited operating area (the foregoing hatched area), which makes it impossible to secure a large practical operating area.